In accordance with a file migration in general, a file that has been stored into a first storage apparatus is migrated to a second storage apparatus. For instance, in accordance with Patent Literature 1 and Patent Literature 2, a migration of a file can be executed in such a manner that a storage cost of data is reduced while a convenience is maintained by storing a file that is provided with a high access frequency into a storage apparatus with a high cost and a high speed and by storing a file that is provided with a low access frequency into a storage apparatus with a low cost and a low speed.